The objective of this project is to study the vitamin K-dependent formation of gamma-carboxyglutamate residues in hepatic precursor proteins. This reaction has been shown to occur in the production of plasma clotting factors II, VII, IX, and X as well as other plasma proteins of unknown function (proteins, C, S and Z) all of which are dependent on vitamin K. We have found that the product of the vitamin K-dependent carboxylation of prothrombin precursor(s) is a protein with the same molecular weight as prothrombin but an isoelectric point of 7.2 (vs. 5.0 for mature prothrombin). Studies described in this project are designed to elucidate the events associated with the further processing of the pI 7.2 carboxylated protein that are involved in the maturation of plasma prothrombin prior to secretion from the liver. Also, we have shown that the carboxylation of prothrombin precursor protein accounts for only about 25% of the vitamin K-dependent incorporation of H14CO3 into precursor proteins in the liver. The properties and functions of the vitamin K-dependent proteins other than prothrombin (i.e., those that incorporate greater than 70% of the H14CO3) will also be investigated as part of this project.